Vehicles and mobile machines generally have a power source such as an internal combustion engine or electric motor, a transmission to transmit drive power to move the vehicle or machine, and a mechanism to selectively transfer rotational torque from the power source to the transmission. In some approaches, the mechanism to selectively transfer rotational torque from the power source to the transmission includes a manual clutch. Manual clutches are efficient. However, operation of manual clutches requires extra effort and added operational oversight by the vehicle operators. Such extra effort and added operational oversight can be less desirable as they can, for example, reduce the operators' efficiency.
An alternative mechanism for transferring rotational torque from the power source to the transmission is a torque converter. A torque converter is generally a hydrodynamic fluid coupling that transfers the rotational torque from a power source to a driven load such as a transmission. The torque converter multiplies the torque from the power source and transfers the torque to the transmission until a speed of an output shaft from the torque converter to the transmission approaches the speed of the shaft of the power source supplying the rotational torque. U.S. Pat. Appl. Publ. No. 2014/0113767 to Jawalkar Nagaraj et al. discloses a torque converter that includes a prime mover input and an impeller configured to rotate in response to the prime mover input. The torque converter further includes a turbine arranged with the impeller and configured to rotate in response to rotation of the impeller, a stator arranged with the impeller and the turbine, and a stator clutch configured to allow rotation of the stator in a first mode and configured to limit rotation of the stator in a second mode. The torque converter further includes a stator clutch actuator configured to activate and deactivate the stator clutch to place the stator clutch in the second mode during particular operations and to place the stator clutch in the first mode otherwise. The reference further discloses a vehicle and a process of converting torque for operation of a vehicle.
However, torque converters are typically less efficient and result in worse fuel economy due to hydraulic losses and the like in comparison to mechanical clutches. Additionally, torque converters in larger vehicle applications require a great deal of torque transfer that can exasperate these problems. Moreover, due to the increased torque requirements of larger vehicles, larger size torque converters are typically required, thereby increasing the cost of production and increasing the space required to house the torque converters and transmissions. Current torque converter designs can also cause excessive torques on the power sources in vehicles and machines that operate on graded surfaces. In view of this, opportunities exist for improvement in the efficiency, fuel economy, size and cost of torque converters, and for reductions the hydraulic losses that exist in torque converters.